1. Field of Invention
The present invention relates to a paper pickup mechanism, and more particularly, to a paper pickup mechanism that provides an equal pickup force under different paper loads, and operates with high precision.
2. Related Art
Usually, a paper pickup mechanism of various types such as a copy machine, a fax machine and a printer has two rubber rollers respectively with high coefficients of friction. One of the rubber rollers is a pickup roller and the other is a feed roller. A topmost paper of the paper load stack is picked by the pickup roller and conveyed to a printing module by a feed roller.
In a traditional paper pickup mechanism that uses a pickup roller to pick up paper, driving energy is usually dissipated through the gear mechanism, and noise is produced due to the friction between two contacting rollers when the papers are transmitted. Therefore, a reduced number of rollers are preferable to reduce inter-roller friction. Furthermore, multi-feeds or feed failure may occur due to weight, density or stiffness of papers.
The rollers may be movable for automatic compensation of the pickup roller. One common approach is to mount the pickup roller at one swing arm or at one end of a set of gears, as disclosed in U.S. Pat. No. 5,527,026. This can automatically compensate the pickup force for different types of papers. However, for one type of paper, the swing range of the pickup roller, being mounted at one swing arm and operating under a different paper load, must be large. This mount provides non-uniform pickup forces, which results in unsatisfactory operational precision.